1. Field of the Invention
The present invention relates to a positioning stage. More specifically, it relates to a mechanism for an accurate movement control while resting a workpiece thereon during accurate measurement by microscope inspection, optical measurement etc.
2. Description of Related Art
Conventionally, during microscope inspection etc., a workpiece is put on a cross-travel stage and is moved so that a portion of interest comes within a predetermined measurement area located on an extension of an objective. For measurement, the portion of interest has to be accurately moved little by little.
In view of the above requirement, the portion of the stage for the workpiece to be put on is arranged to be movable in X and Y directions and a driving mechanism capable of accurate feeding movement little by little is provided to control movement thereof.
For such driving mechanism of the stage, a rack-and-pinion mechanism and a feeding mechanism using a rail and a friction gear can be used. However, on account of problem relating to accuracy and movement smoothness, another type of feeding mechanism using a belt and a pulley recently comes into use (see Japanese Patent Publication No. Hei 7-1340, Japanese Patent Laid-Open Publication No. Hei 4-31814 and Japanese Patent Laid-Open Publication No. Hei 9-113814).
The feeding mechanism with a belt and a pulley, for moving a table for a workpiece to be put on relative to a base, has a pair of pulley supported on, for instance, a base side and an endless belt is wound between the pulleys. One table is supported movably relative to the base and is associated with a part of the belt through a joint. Ordinarily, the table is supported by a guide rail for guiding the table in an extension direction of the belt.
A manipulation knob is connected to a shaft of one of the pulleys and the pulley is rotated by rotating the knob, thus circulatingly rotating the endless belt stretched therearound. By thus feeding the belt, the table associated with a joint is also fed, thus feeding the table by the knob.
Incidentally, for quickly feeding the table by directly holding the table in adjusting the portion of interest to the measurement area, a clutch mechanism etc. for releasing the feeding mechanism composed of the belt and the pulley is provided. Ordinarily, the joint of the table relative to the belt is released. Specifically, the joint is fixed and released at any position of the belt.
According to the above-described conventional feeding mechanism by the belt and the pulley, following problems arise.
First, it is difficult to simplify the structure of the feeding mechanism and to reduce a size thereof.
In other words, tension has to be applied to the belt to eliminate a slack of the belt and further strong tension is necessary for driving the belt by the pulley. Specifically, in order to transfer the rotation of the pulley to the belt, a predetermined friction is necessary between the pulley and the belt, and further strong tension is necessary for the belt to satisfy the requirement. Accordingly, a structure and strength enough to endure the strong tension of the belt is necessary for the pulley, rotation shaft thereof, support portion thereof etc.
Second, feed of the table cannot be adjusted finely enough.
In other words, since the conventional feeding mechanism by the belt and pulley rotates the pulley by rotating the manipulation knob to drive the belt wound between the pulleys, relationship between a control input of the manipulation knob (circumference thereof) and a feed displacement of the belt (i.e. feed displacement of the table) depends on a radius of the manipulation knob and the pulley. Accordingly, in order to set the feed of the table, the radius of the pulley has to be made small.
However, when the radius of the pulley is reduced, curvature of the belt wound therearound becomes small. And an allowable minimum bend radius for assuring normal operation is determined in advance in view of material thereof. Accordingly, the radius of the pulley cannot be reduced beyond the allowable minimum bend radius, thus unable to sufficiently set the minute feed of the table.
Third, the components cannot be arranged freely enough.
Specifically, in the conventional feeding mechanism by the belt and the pulley, since the manipulation knob is connected to the shaft of the pulley, the disposition of the components is restricted by the position of the pulley. Operability of the manipulation knob is not so good because the pulley is ordinarily disposed at both ends of the stretched belt (end of the feeding mechanism). However, as described above, since the location is restricted by the position of the pulley, it cannot be easily changed. Though the position can be changed using other transmission means, the mechanism can be so complicated.
Further, the feeding mechanism by the belt and the pulley may be provided in crosswise two directions for moving biaxially, i.e. X and Y-axis directions in the conventional stage drive mechanism. Further, for improving operability, the manipulation knob of respective shafts is formed in coaxial double cylindrical shape. However, as described above, the location of the manipulation knob is restricted by the pulley position at the end of the feeding mechanism, and the respective manipulation knobs have to be adjusted at the same position in order to form the manipulation knob in the double cylindrical form. Accordingly, the feeding mechanism of respective directions is only allowed to cross at the end thereof. More specifically, the feeding mechanism can only be disposed at a periphery of respective tables and the space at central portion cannot be used.
An object of the present invention is to provide a positioning stage capable of simplifying and size-reducing a structure thereof, improving feeding accuracy of the table and freely arranging respective components.
The present invention is a positioning stage having: a table for a workpiece to be rested; a base for supporting the table; and a feeding mechanism interposed between the table and the base for moving the table relative to the base in a predetermined movement direction along a surface of the table, in which the feeding mechanism has: a pair of pulley supported by either one of the table and the base; a loop-shaped drive force transmission member stretched between the pair of pulley, at least a part of the drive force transmission member extending in the movement direction; a joint for connecting the other one of the table and the base with a part of the drive force transmission member extending in the movement direction; and a pinch mechanism provided to the either one of the table and the base for holding a part of the drive force transmission member to drive the drive force transmission member.
According to the above arrangement, the drive force transmission member is driven not by the pulley portion but by the pinch mechanism separately provided (a combination of a rotation drive capstan and a pinch roller rotating by being pressed). The pinch mechanism holds the drive force transmission member (belt, wire, chain and other flexible elongated member) to secure transmission of the drive force. Accordingly the strong tension of the drive force transmission member necessary for transmitting the rotation of the pulley to the drive force transmission member is not required, thus size-reducing and simplifying the portion adjacent to the pulley.
Further, since the drive force transmission member is not wound to the roller of the pinch mechanism (driving side, capstan), the allowable minimum bend radius does not influence on the pinch mechanism. Accordingly, the feed can be minutely set by reducing the radius of the roller of the pinch mechanism.
Further, since the pinch mechanism can be disposed to any section of the path of the drive force transmission member, the operation knob etc. for controlling feed operation can be more freely disposed. Further, when the feeding mechanism is provided in two directions crosswise, the feeding mechanism can be crossed at any desired position, thus more freely disposing the feeding mechanism.
In the present invention, the pinch mechanism may preferably have a drive roller (a capstan) and a follower roller (pinch roller) sandwiching the drive force transmission member, and a manipulation knob capable of being rotatably operated from an outside may preferably be connected to the drive roller.
Accordingly, the pinch mechanism can be directly driven, thereby effectively size-reducing and simplifying the structure.
In the present invention, the pinch mechanism may have a release mechanism capable of releasing hold and drive of the drive force transmission member by associating and separating the follower roller relative to the drive roller.
Accordingly, the release mechanism can be constructed with a simple structure utilizing the characteristics of the pinch mechanism.
Incidentally, for associating and separating the follower roller relative to the drive roller of the release mechanism, the follower roller may be supported by a movable plate, one end of the movable plate being rotatably supported and the other end of the movable plate being connected with a cable to be pushed and pulled. For operating the release cable, a release lever may be provided to a manual-operation grip provided to one end of the table so that the cable is pulled by the release lever and is pushed back by a spring.
In the present invention, a sub-table may be interposed between the base and the table, first feeding mechanism may be disposed between the base and the sub-table, and second feeding mechanism may be disposed between the sub-table and the table.
Accordingly, bi-directional movement such as in X and Y-axis directions can be easily conducted.
Incidentally, other guiding mechanism may be additionally disposed between the base and the table and between the sub-table and the table.
Further, it is not requisite that the first and the second feeding mechanism exist between the base and the sub-table and between the sub-table and the table. For instance, the first feeding mechanism may be provided outside the base and the sub-table for relatively moving the base and the sub-table.
In the present invention, the first and the second feeding mechanisms may preferably be disposed in two movement directions mutually crosswise, the feeding mechanisms mutually crossing at an intermediate section thereof.
Accordingly, since the pinch mechanism of the first and the second feeding mechanisms concentrates to one location where the first and the second feeding mechanisms can be controlled, the operability can be improved.
In the present invention, the pinch mechanism of the first and the second feeding mechanism with the movement direction thereof crossed may preferably have a drive roller and a follower roller sandwiching the drive force transmission member, the drive roller of the first and the second feeding mechanisms being coaxially disposed, and a manipulation knob for controllably rotating the respective drive rollers being coaxially formed.
Accordingly, the first and the second feeding mechanisms can be controlled at one location by the coaxial manipulation knob, thus improving operability.
Further, in the present invention, the manipulation knob may preferably have: a stationary shaft; first manipulation tab coaxially and rotatably disposed to the stationary shaft to be connected to one of the drive rollers; second manipulation tab coaxially and rotatably disposed to the stationary shaft to be connected to the other one of the drive rollers; and a holding member interposed between the stationary shaft and either one of the first and the second manipulation tab for applying holding force to hold the first or the second manipulation tab at a current position.
Accordingly, an appropriate holding force is applied to the respective manipulation knobs so that an unprepared movement of the stage caused by vibration etc. can be prevented and an appropriate weight is applied to a minute operation of the stage, thereby facilitating minute operation control.